1. FIELD OF THE INVENTION
The invention relates generally to highly mobile, vertically erected masts for drilling rigs. More particularly, the invention relates to a method and apparatus for erecting a multi-sectioned vertically disposed mast on a drill platform using the existing platform drawworks.
2. DESCRIPTION OF THE RELATED ART
Different types of masts have been devised for use in the drilling industry. In offshore or remote area drilling operations, it is desirable for such masts to be portable from one well to the next. Portability is also preferred for offshore operations that may be subjected to severe weather. In such cases, it is desirable to be able to quickly dismantle the mast to avoid potential damage, and even destruction.
Drillers have typically used two types of portable or semi-portable masts in offshore or remote drilling environments. The first type consists of a folded mast which typically has a lower end pivotally connected to either the drill platform or, in the case of a truck mounted mast, the rear of the truck. In raising, either by the available platform crane, drawworks, or a separate winch, the folding mast pivots from a horizontal position to a vertical position, where it is typically secured.
The second type of portable or semi-portable mast known in the art consists of a two- or three-section telescoping mast wherein the upper section is telescoped into the lower section and the entire assembly is transported from one location to the next. Such masts are typically transported horizontally to the drill platform and jackknifed into a vertical position. From this vertical position, the sections are then extended telescopically.
Both the folding and telescoping masts, while providing some mobility and stability during transportation, have certain disadvantages. In offshore or remote area drilling, there may only be small capacity cranes available for mast erection. Mast structures that telescope into a single assembly can exceed the weight and size limitations of the crane. In the case of truck-mounted folding masts, the overall length of the mast may be limited by the length of the truck.
U.S. Pat. No. 4,134,237, issued to Armstrong, describes a multi-sectioned telescoping mast, wherein the upper-most mast section is inserted into the lower-most mast section which is fixed vertically to the drilling platform. The uppermost mast section is raised within the lower mast section by a cable, which is connected to a spool driven by the platform drawworks. The intermediate mast section is inserted and secured to the lower end of the uppermost mast section. While the uppermost and intermediate masts sections are held in position, the cable is lowered to engage the lower end of the intermediate mast section and the drawworks is actuated to raise the uppermost and intermediate mast sections to enable the lower end of the intermediate mast section to be coupled to the upper end of the lowermost mast section.
The Armstrong device, while apparently solving some of the problems of the prior art devices, also has some inherent disadvantages. The Armstrong device requires a special cable to be placed on the drawworks spool. The drawworks spool has a grooved surface which may be damaged if the dimensions of the special cable do not match the dimensions of the spool grooves. Moreover, the Armstrong device requires the crown block and travelling block to be strung with cable after the mast is erected. This is a cumbersome procedure since the crown block may be over a hundred feet above the drilling floor. In addition, the upper sections of the Armstrong mast are coupled to each other and to the lowermost section with an offset. Therefore, the load on the mast must be carried by an offset connection that couples together the upper sections and the lowermost section.
The present invention is directed to overcoming or minimizing one or more of the problems discussed above.